Dynamic allocation of radio resources in a packet switched communications-system

ABSTRACT

Voice and/or image data packets are transferred by a packet handler between user stations in a GSM-type mobile communications system using a General Packet Radio Service (GPRS) data link. Control data for controlling a call is stored in a data store accessible by the packet handler. The control data identifies call participants and the identity of a participant who has currently seized the call. A mobile station capable of video conferencing is operable in a half-duplex video conferencing mode, in which intermittent transmission of video data is controlled by depression of a transmit button.

FIELD OF INVENTION

This invention relates to mobile communications, such as cellularcommunications. The invention is particularly, but not exclusively,applicable to GSM-type mobile communications systems.

BACKGROUND OF THE INVENTION

An example of a cellular communications system which provides voicedispatch services is the Motorola (trademark) integrated digitalenhanced network, or iDEN (trademark), system. The system includesEnhanced Base Transceiver Systems (EBTSs) at cell sites which linkmobile terminals to the fixed network equipment via a TDMA radiointerface, and which are connected to controlling base stationcontrollers (BSCs). The BSCs provide a link with a mobile switchingcentre (MSC) which provides conventional circuit switching with a publicservices telephone network (PSTN), and a Metro Packet Switch (MPS) whichprovides switching for the dispatch services. A Dispatch ApplicationProcessor (DAP) coordinates and controls dispatch communications, byregistering the identifications and locations of mobile terminals activein the system.

The iDEN system provides both voice dispatch services, circuit-switchedcall services and other data communications services, such as a shortmessage service.

U.S. Pat. No. 5,416,770 describes a voice dispatch cellularcommunications system, in which audio data packets are transported viaframe relay links. Communication is established between a plurality ofcommunication units by replicating the transmitted data packets, anddistributing the replicated packets to identified target base stations.

U.S. Pat. No. 5,448,620 describes a mobile terminal which is operable inboth a voice dispatch mode and a telephone interconnect mode.

A known GSM network, referred to as a public land mobile network (PLMN),is schematically illustrated in FIG. 1. A mobile switching centre (MSC)2 is connected via communication links to a number of base stationcontroller (BSCs) 4. The BSCs 4 are dispersed geographically acrossareas served by the mobile switching centre 2. Each BSC 4 controls oneor more base transceiver stations (BTSs) 6 located remote from, andconnected by further communication links to, the BSC. Each BTS 6transmits radio signals to, and receives radio signals from, mobilestations 8 which are in an area served by that BTS. That area isreferred to as a “cell”. A GSM network is provided with a large numberof such cells, which are ideally contiguous to provide continuouscoverage over the whole network territory.

A mobile switching centre 2 is connected via communications links toother mobile switching centres in the remainder of the mobilecommunications network 10, and to other networks such as a publicservice telephone network (PSTN), which is not illustrated. The mobileswitching centre 2 is provided with a home location register (HLR) 12which is a database storing subscriber authentication data including theinternational mobile subscriber identity (IMSI) which is unique to eachmobile station 8. The IMSI is also stored in the mobile station in asubscriber identity module (SIM) along with other subscriber-specificinformation.

The mobile switching centre is also provided with a visitor locationregister (VLR) 14 which is a database temporarily storing subscriberauthentication data for mobile stations active in its area.

GSM was originally designed to support full duplex, circuit-switchedvoice calls.

A new element of functionality is added in the GSM Phase 2+TechnicalSpecifications, which is referred to as the advanced speech call items(ASCI). This provides for group calls which are broadcast to memberswithin a group. In order to establish a broadcast group call, anoriginating mobile station sends a service request to the MSC,containing the requested group identity. The MSC authenticates thesubscriber using the VLR.

If the authentication check is successful, the MSC requestsidentification data for the members of the group from a group callregister. With this information, the MSC sets up connections between thereceiving mobile stations and a group call dispatcher. Each of the cellsin which recipient mobile stations are located pages a notification,containing the identity of the group being called and the description ofthe channel allocated for the group call broadcast. The group calldispatcher transmits the group call data to each of those cells, forbroadcast on the allocated channels.

A further element of functionality which is added to GSM in the GSMPhase 2+ Technical Specification is the general packet radio service(GPRS).

GPRS provides a packet-mode service to transfer high-speed and low-speeddata and signalling efficiently over the GSM radio network. It isdesigned to support a range of types of data transfer, from intermittentand bursty data transfers to the occasional transfer of large volumes ofdata. It is envisaged for use in Internet services, e-mail and otherdata services.

GPRS includes facilities for both point to point (PTP) and point tomultipoint (PTM) data packet transfer. In PTM data packet transfer, thedata packets are broadcast in all of the cells in a defined geographicalarea. In each case, GPRS transmits the data packets transparently,insofar as other than ensuring that the data packets are receivedcorrectly at their destination, there is no knowledge of the contents ofthe data packets on the network side.

The GPRS radio interface is placed in a flexible number of TDMA timeslots of the GSM physical radio interface used for circuit-switchedtraffic channels and signalling channels. The same GPRS radio resourcesare shared by all mobile stations in a cell, the radio resources beingreserved by or for mobile stations only when there are data packets tobe sent.

The packet-oriented network infrastructure includes a packet datanetwork having packet switches in the form of GPRS support nodes (GSNs)interconnected by a GPRS backbone network, and including a gateway GPRSsupport node (GGSN) for routing data packets to and from an externalpacket data protocol (PDP) network, using a protocol such as TCP/IP,X.25 and the like.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provideda method of controlling communication between user stations using amobile communications system having a radio interface, said methodcomprising:

-   -   providing a data packet handler connected to a packet data        network;    -   holding control data, indicating a state of a call between a        first user station and a second user station;    -   dynamically assigning radio resources for the transfer of data        packets carrying call data for said call over said radio        interface, such that the amount of radio resources assigned        varies in accordance with the amount of call data to be        transferred at different points in said call; and    -   controlling the transfer of data packets between said first and        second user stations, using said data packet handler, in        accordance with said control data.

The state of a call may be held in a network-side store, to allowcontrol of the communication between the mobile stations. Thefunctionality provided by a packet data network, and the nature of radioresource allocation and control, is such that data transfer is possiblethroughout a call, even when the transfer of data is intermittent,without requiring an ongoing circuit-switched connection between theuser stations. The data transferred may be voice call data, or videocall data.

In accordance with a further aspect of the invention there is provided amethod of handling the transfer of data in a GSM-type mobilecommunications system, said method comprising:

-   -   receiving a first data packet from a first user station, said        first data packet containing a recipient ID;    -   mapping said recipient ID to a packet network protocol address        whereby routing to a second user station is identified by a        gateway GPRS support node; and    -   transmitting a second data packet to said gateway GPRS support        node, said second data packet containing said packet network        protocol address.

This aspect provides functionality allowing the transfer of data packetsbetween user stations using GPRS, wherein a known recipient ID, ratherthan a packet network protocol address (which may be only temporarilyallocated), may be used by the first user station to identify the seconduser station.

In accordance with a further aspect of the invention there is provided amethod of conducting communications between user stations using a mobilecommunications system, each said user station comprising a camera forpicking up an image of the user and a display for displaying an image ofa remote party, said method comprising establishing a data transferconnection between said user stations, and controlling said connectionin a half-duplex mode such that a user station may perform one of eitheronly receiving or only transmitting image data for a first periodsufficient to receive or transmit image data forming an image, andperform the other of only receiving or only transmitting video imagedata for a second period following said first period and sufficient totransmit or receive image data forming an image.

In accordance with a still further aspect of the invention there isprovided a mobile station adapted to conduct video image communications,said mobile terminal having a half-duplex communications mode controlledby a data processor which in that mode prevents the transmission ofvideo image data during the reception of video image data and whichallows the transmission of video image data during a period selected bya user.

These aspects provide a method of conducting communications, and amobile station, which may be used for video conferencing in a novel andadvantageous fashion. By limiting the communications to a half-duplexmode, the bandwidth and mobile station power requirements needed for thecall may be reduced.

In addition, operation in a dispatch communications mode, wherein thevideo data is distributed amongst groups of recipients which may eachboth transmit and receive data, is possible. One party may seize thecall to transmit video data which is received by the remainingparticipants. The call may then be subsequently seized by differentparticipants.

Further aspects of the invention are defined in the appended claims, andfeatures thereof will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of a known public land mobilenetwork;

FIG. 2 is a schematic block diagram of a mobile station in accordancewith a first embodiment of the invention;

FIG. 3 is a schematic block diagram of a mobile communications networkarranged in accordance with the present invention;

FIG. 4 is a schematic illustration of a call group record used inconnection with embodiments of the present invention;

FIG. 5 is a schematic illustration of a mobile subscriber record storein connection with embodiments of the present invention;

FIGS. 6, 7 and 9 are flow diagrams illustrating procedures carried outby mobile stations in accordance with embodiments of the presentinvention;

FIGS. 8, 10 and 11 are flow diagrams illustrating procedures carried outby a data packet handler in accordance with embodiments of theinvention; and

FIG. 12 is a schematic block diagram of a second embodiment of a mobilestation in accordance with the present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

Referring to FIG. 2, a GSM-compliant mobile station 8 in accordance withan embodiment of the present invention is a handset which comprises atransmit/receive aerial 16, a radio frequency transceiver 18, a GPRSmodule 19 which includes a packetiser/depacketiser and buffer store, aspeech coder/decoder 20 connected to a loudspeaker 22 and a microphone24, a processor circuit 26 and its associated memory 28, an LCD display30, a manual input port (keypad) 32 and a push-to-talk button 34. Themobile station is connected to a removable subscriber identity module(SIM) not shown, via electrical contacts.

FIG. 3 is a schematic illustration of a GSM-type PLMN arranged inaccordance with an embodiment of the present invention. The PLMNincludes GPRS support nodes, including one or more serving GPRS supportnodes (SGSNs) 40, and a gateway GPRS support node (GGSN) 44. The PLMNincludes all of the components described in relation to FIG. 1.

The mobile station 8 may conduct circuit-switched calls, via the MSC 2,immediately after camping on to a serving cell, as in the prior art.

The GGSN 44 is the node provided to interface the PLMN with an externalpacket data network 46, such as a TCP/IP network. It contains routinginformation for active GPRS users in the PLMN, which is used to transmitdata packets, referred to as packet data protocol protocol data units(PDP PDUs) to the current point of attachment of a mobile station in thePLMN from the packet data network. The GGSN provides a mapping functionfor mapping a packet data protocol (PDP) address, whereby a mobile useris identified in the packet data network 46, to a mobile stationidentity, whereby the mobile user is identified in the PLMN. The PDPaddress of a mobile user conforms with the standard addressing scheme ofthe respective network layer service used in the packet data network 46,for example an IP version 4 address, an IP version 6 address or an X.121address.

A mobile user may be allocated a permanent, or “static” PDP address,which is stored in the mobile station 8 and the HLR 12, or may beallowed to request a temporary, or “dynamic” PDP address, which isallocated by the GGSN 44 on request.

The SGSNs 40, 42 are referred to as serving GPRS support nodes, in thatthese nodes are those which serve mobile stations 8 in their routingareas. On logon to the GPRS service of a mobile station, the SGSNestablishes a mobility management context containing informationpertaining to mobility and security for the mobile station. The SGSNalso establishes a routing context, referred to in GPRS as a “PDPcontext”, with the GGSN 44 to be used by the mobile station 8 to accessthe packet data network 46.

The SGSN and the GGSN functionalities may be combined in the samephysical node, or they may reside in different physical nodes.

The packet data network 46 may be the public Internet, an intranetconnection or a leased line. The packet data network 46 may also provideconnections with other elements, such as a GGSN 56 of other PLMNs orfixed terminals 58.

Thus, with the additional functionality of the SGSNs 40 and the GGSN 44in the PLMN, and the GPRS module 19 in the mobile stations 8, the mobilenetworks and users are GPRS enabled, whereby the mobile users maytransmit and receive packet mode data. For example, the mobile user mayuse the mobile station 8 in order to access Web pages, using terminalequipment attached to the mobile station 8, on the public Internet, viathe gateway functionality provided by the GGSN 44 and the packet modetransfer functionality provided in the remainder of the networkincluding the SGSNs 40, 42, the BSCs 4, the BTSs 6 and the GPRS radiointerface.

The GPRS radio interface is described in GSM 03.64 Version 5.1.0,entitled “Digital Cellular Communications System (Phase 2+)”; GeneralPacket Radio Service (GPRS); Overall Description of the GPRS RadioInterface; Stage 2, published by European Telecommunications StandardInstitute, the contents of which are incorporated herein by reference.

The GPRS architecture and transmission mechanism, mobility managementfunctionality, network management functionality, radio resourcefunctionality, packet routing and transfer functionality, transmissionand information storage using GPRS are described in GSM 03.60 Version5.2.0, entitled “Digital Cellular Telecommunications System (Phase 2+)”;General Packet Radio Service (GPRS); Service Description; Stage 2,published by the European Telecommunications Standard Institute, thecontents of which are incorporated herein by reference.

In addition to the standard GPRS infrastructure, this embodiment ofmobile communications system of the present invention includes adispatch packet handler 48, a packet store 50, a packet user database(PUD) 52 and a service management terminal 54.

The packet handler 48 is responsible for setting up virtual connectionsbetween GPRS users in the PLMN, and for copying packets when datapackets are to be distributed to groups of users.

The packet store 50 is responsible for storing data packets which areintended for distribution to GPRS users within the PLMN who areuncontactable via GPRS at the time of receipt of data packets for theuncontactable user at the packet handler 48.

The packet user database 52 holds service data records used by thepacket handler 48 to set up and manage virtual connections between GPRSusers in the PLMN. The service management terminal 54 is used to updatethe service data in the PUD 52.

The PUD 52 holds call group records for identifying the members of acall group. Referring to FIG. 4, which shows an exemplary call grouprecord, a field for a single call group is identified by a call group IDcontaining fields 60, two or more mobile station IDs, MSID1, MSID2 . . .MSIDn are contained in fields 62, and each mobile station ID field 62has an associated call seize field 64 flagged to indicate that theassociated mobile station has currently seized the call group.

In addition to call group records, the packet user database 52 storesidentification records for each mobile subscriber in the PLMN who has avalid subscription to the GPRS virtual connection service of the presentinvention. Referring to FIG. 5, each such subscriber has a mobilesubscriber record including a field 66 containing a permanent mobilestation ID 66, a field 68 for containing an allocated PDP address, ifcurrent, and a field 70 for containing a call group ID, if current, forthe mobile subscriber in question. If the PDP address field 68 is empty,this indicates that the mobile station is not currently attached to theGPRS service. If the current call group ID field 70 is empty, thisindicates that the subscriber is not currently participating in a GPRSvirtual connection call.

FIG. 6 illustrates procedures carried out in the mobile station 8 inorder to participate in the GPRS virtual connection service of thepresent invention.

In order to utilise the GPRS service, the user initiates a GPRS logoriprocedure from the mobile station 8, step 100.

The GPRS logon signalling procedure is described in GSM 03.60 V.5.2.0,part 6.5 entitled “Attach Function”, which part is incorporated hereinspecifically by reference. This part also refers to part 9.2.2 entitled“Activation Procedures” of the same document, which describes the PDPcontext activation procedure at logon, which part is also incorporatedherein specifically by reference.

After having executed GPRS attach, the mobile station is in a “readystate”, in which packet transfer may occur via the GPRS radio interfacebetween the mobile station 8 and the PLMN, and mobility managementcontexts are established in the mobile station and the SGSN 40. Themobile station then activates its PDP context, by transmitting an‘Activate PDP Context’ request to the SGSN 40. If the mobile station isusing a static PDP address, it transmits its static PDP address in the‘Activate PDP Context’ request.

The SGSN 40 queries the HLR 12, in which GPRS subscription informationis held for the subscriber, in order to check that the mobile station 8is allowed to activate the PDP address contained in the request. Ifallowed, the SGSN transmits a ‘Create PDP Context’ request to the GGSN44, which creates a new entry in a PDP context table held in the HLR 12on behalf of the GGSN 44. This PDP context table includes the mobilestation identity and the PDP address allocated to the mobile station,allowing the GGSN 44 to map between these two identifies and therebyroute data packets between the SGSN 40 and the packet data network 46.

If the mobile station 8 is not using a static PDP address, the ‘CreatePDP Context’ request sent by the SGSN 40 to the GGSN 44 results in theGGSN allocating a dynamic PDP address, which is signalled, via the SGSN40, to the mobile station 8.

Whether the mobile station is using a static PDP address or a dynamicPDP address, the mobile station 8 is provided in each case with a PDPaddress whereby routing for packets arriving from the packet datanetwork 46 is identified. Routing within the PLMN is provided by theGPRS data packet encapsulation procedure, which encapsulation is removedfrom the data packets at the GGSN 44 and the mobile station 8. Theencapsulation function is described in part 9.6 of the document GSM03.60 V.5.2.0, which part is specifically incorporated herein byreference. GPRS transparently supports the transfer of PDP PDUs betweenexternal networks and the mobile stations. One encapsulation scheme(referred to herein as GSN—GSN encapsulation) is used for the GPRSbackbone network between GSNs in the PLMN, and one (referred to hereinas SGSN-MS encapsulation) is used for the GPRS connection between theSGSN 40 and the mobile station 8.

The GGSN 44 is arranged such that once the PDP context entry has beenmade in the HLR 12 by the GGSN 44 for a newly logged-on GPRS user, theGGSN 44 transmits a logon message to the packet handler, informing thepacket handler 48 of the mapping between the mobile station identity,held in field 66 of the mobile station record held in the PUD 52,whereby the user is permanently identified in the PLMN, and theallocated PDP address. On receipt of the logon message, the packethandler 48 enters the allocated PDP address in field 68 of the mobilesubscriber record for the subscriber in question.

Once logged-on to the GPRS service, the mobile station may transmit datapackets to, and receive data packets from, the packet handler 48.

Data packets originated in the mobile station 8 are transmitted over theradio interface and via the BTS 6 and the BSC 4 to the SGSN 40. When theSGSN 40 has received a packet completely and correctly, it GSN—GSNencapsulates the packet into a GPRS backbone network packet which issent to the GGSN 44. The GGSN 44 decapsulates the packet and forwardsthe data packet, using the PDP address allocated to the sender as thepacket originating address in a header portion of the data packet, tothe packet handler 48.

Data packets originated in the packet handier 48 are transmitted to amobile station 8 by attaching the allocated PDP address, which is heldin the PUD 52 for the recipient, to the data packet as a destinationaddress in a header portion of the data packet. The data packet istransmitted, via the packet data network 46, to the GGSN 44. In the GGSN44, the PDP address of the receiver is read, and the SGSN which isserving the mobile station is identified from routing data held in theHLR 12. The data packet is then GSN—GSN encapsulated and sent to theidentified SGSN. The SGSN strips the GPS backbone network encapsulation,and the original data packet is SGSN-MS encapsulated and transmitted tothe mobile station 8 via the BSC 4, BTS 6 and GPRS radio interface.

When the mobile station 8 receives the packet, it removes the SGSN-MSencapsulation and processes the data packet. If the data packet is avoice data packet, a sequence of packets are reassembled and a voicesignal is generated in the mobile terminal.

The user may set up a call by selecting, via a man machine interface,e.g. the keypad 32, of the mobile station 8, from a stored list of callgroups of which the mobile user is a member, a call group for which avirtual connection is to be established. Such selection is part of theinitiation of a call set up-transmit procedure, step 102, which is to bedescribed below in relation to FIG. 7.

Once logged-on to the GPRS service, the mobile station 8 is able toreceive call set up-receive requests from the packet handler 48, whichinitiates a procedure to be described below in relation to FIG. 9. Onceparticipating in a call, the mobile station 8 is also able to start toreceive call data packets, step 106, and start to transmit call datapackets, step 108, to be described below in relation to FIGS. 7 and 8.In addition, a user has the facility to end participation in a call, byinteraction with a man machine interface, e.g. the keypad 32, of themobile station 8, step 110, which causes the mobile station to transmitan end participation request to the packet handler 48, step 112, and todelete the call group ID from its current call record, step 114.

The user may also logoff the GPRS service if desired, step 116, whichresults in logoff procedures carried out by the mobile station 8, step118, including the deletion of the allocated PDP address for thesubscriber in the HLR records stored by the GGSN 44. The GGSN 44 isarranged such that, on receiving a logoff message from the SGSN 40, theGGSN 44 also transmits a logoff message to the packet handler 48, whichresults in the deletion of the previously allocated PDP address from thePDP address field 68 in the mobile subscriber record held for thesubscriber in the PUD 52.

Referring to FIG. 7, when a user first instructs the mobile station 8 toset up a call for a particular call group, by the depression of the PTTbutton 34 after the selection of a call group from a list of call groupsstored in the SIM of the mobile station 8, the mobile station 8transmits a set up request, containing the selected call group ID, asone or more GPRS data packets to the packet handler 48, step 200. Thecall handler conducts procedures to be described below in relation toFIG. 8, and, depending on the success of those call set up procedures,the packet handler 48 may transmit a set up confirmation message to themobile station within a time-out set within the mobile station 8, ornot. If the call set up confirmation is not received within the time-outat the mobile station, step 202, the mobile station returns to thegeneral GPRS logged-on state, and the mobile station 8 may retry bytransmitting a further call set up request.

If the set up confirmation message is received from the packet handler48 within the time-out, the mobile station 8 provides an audio or visualindication to the user that a virtual connection has been established,step 204. In addition, the mobile station places the call group IDselected by the user in a current call record, step 206.

At this point, the user may transmit voice data by speaking into themicrophone 24 as long as the PTT button 34 remains depressed. The speechsignals are coded by the codec 20 and passed on to the GPRS module 19,in which the speech data is packetised and buffered, step 208, andSGSN-MS encapsulated for transmission over the GPRS radio interface bythe radio frequency transceiver 18 and onward to the packet handler 48,step 210.

As soon as the PTT button 34 is released, step 212, the mobile station 8generates a transmit end message, in the form of a data packet, which istransmitted to the packet handler 48, step 214.

Referring to FIG. 8, on receipt of a call set up request, step 300, thepacket handler 48 retrieves, using the call group ID contained in thecall set up request, the recipient records from the PUD 52 whichidentify the recipients which are currently available for receipt of acall set up message, step 302. Each mobile station in the call grouprecord has an associated mobile station record which is identified bythe mobile station ID contained in the call group record. For eachmobile station record which contains a PDP address and no current callgroup ID, a set up message is transmitted by the packet handler, usingthe PDP address retrieved for the mobile station in question, step 304.Mobile station records which contain either no allocated PDP address orcontain a current call group ID are placed in a call waiting list in thePUD 52, and voice data packets subsequently received for the same callgroup are forwarded to the packet store 50 for storage. In the case of apotential recipient not yet logged-on to the GPRS service, on receipt ofnotification at the packet handler 48 that the recipients havesubsequently logged-on, a set up message is then transmitted, to allowthe previously unavailable recipient to receive the data held in thepacket store 50 if desired. Similarly, if a potential recipient isunavailable because the recipient is engaged in a different call, oncethe packet handler 48 receives an end participation message from thepotential recipient for the previous call, the packet handler respondsby transmitting a set up message to the previously unavailablerecipient, to allow the recipient to receive data previously held in thepacket store 50 if desired.

If the packet handler receives no acknowledgements from the availablerecipients to which set up messages have been sent within a time-out setin the packet handler 48, step 306, the call set up has beenunsuccessful and the packet handler ends the procedure without storingany references to the call set up attempt either in the PUD 52 or in thepacket store 50.

Otherwise, the packet handler 48 enters the call group ID into thecurrent call group field 70 for both the call set up request sender andthe call set up message recipients which have acknowledged call set up,step 308. As further recipients acknowledge call set up, the currentcall group ID is entered into the call group ID field 70 for each of theadditional recipients.

In addition, the packet handler 48 sets the call seize flag in the field64 of the call group record which corresponds to the mobile station IDof the call set up request sender, and transmits a set up confirmationmessage to the sender, step 310, indicating that the sender is now ableto transmit voice data, step 310.

Once the sender receives the set up confirmation message, as describedin relation to FIG. 7, the sender presses the PTT button 34 and beginsthe transmission of voice data packets, which are received at the packethandler 48, step 312. If the number of recipients currentlyparticipating in the call exceeds a single recipient, step 314, thepacket handler 48 replicates the contents of each packet for eachrecipient, step 316.

The receive packets are then transmitted to each participatingrecipient, step 318, until such time as an end message is received fromthe voice packet transmitting mobile station 8, step 320. Once the endmessage is received from the sending mobile station 8, an end message istransmitted to each recipient, step 322, and the call seize flag isremoved from field 64 in the call group record corresponding to thesender mobile station ID, in the PUD 52, step 324.

Referring to FIG. 9, when a mobile station 8 receives the set up messagefrom the packet handler 48, step 400, the mobile station 8 displays theidentity of the sender, which is contained in a header portion of thedata packet, including the call group ID and the name of the individualsubscriber, step 402. In response, the recipient may accept the call byinteraction with the man machine interface of the mobile station, step404. If the user does not accept, the mobile station does not respond tothe set up message. Otherwise, the mobile station 8 transmits anacknowledgement to the packet handler 48 and places the call group ID inthe current call record held in the mobile station memory 28, steps 406and 408.

As a result of the acknowledgement received at the packet handler 48,any data packets subsequently transmitted by the voice data sender isthen transmitted, using the virtual connection provided by the packethandler 48, to the recipient mobile station 8, step 410. At therecipient mobile station 8, the data packets are converted into voicedata and output as an audio signal, step 412, until such time as an endmessage is received from the packet handler 48, step 414.

On receipt of the end message, the recipient mobile station provides theuser with an audio or visual indication of the end of receipt of thevoice data packets, step 416, to indicate that the call group may now beseized if desired by the recipient.

In order to seize the call group, following call set up, any participantmay push the PTT button 44 in a period of inactivity, that is to say, inthe case of a previously receiving mobile station, after receipt of atransmit end message as in step 214 and preceding receipt of furthervoice data packets from other parties, and in the case of a previouslytransmitting mobile station, after the user releases the press to talkbutton and before receipt of voice data packets from other parties.

Referring again to FIG. 7, when the mobile station 8 detects pressing ofthe PTT button in this inactive state, the mobile station 8 transmits acall seize request to the packet handler 48, step 216. The call group IDheld in the current call group ID record in the mobile station 8 isincluded in the call seize request message automatically by the mobilestation. The user therefore does not need to re-identify the call groupof the call in which he is currently participating.

If no call seize confirmation is received from the packet handler 48within a time out period set within the mobile station 8, the mobilestation 8 may retry to seize the call at a later stage, by thetransmission of a further call seize request.

If a call seize confirmation message is received from the packet handler48, step 218, an audio or visual indication is provided to the user toindicate success, step 220, after which the user is able to transmit hisvoice to all of the current call group participants by keeping the PTTbutton held down and speaking into the microphone 24 of the mobilestation 8.

Referring to FIG. 10, on receipt of a call seize request, step 500, thepacket handler 48 queries the PUD 52, step 502, in order to determinewhether another participant in the call has current seizure of the callgroup, as will be indicated by a call seize flag held in a field 64 ofthe call group record. If no call seize flag appears in the call grouprecord, the packet handler 48 transmits a call seize confirmationmessage to the sender of the call seize request, step 504, and adds acall seize flag to the field 64 corresponding to the sender in a callgroup record held in the PUD, step 506.

Referring to FIG. 11, on receipt of an end participation request from amobile station of a user currently participating in a call, step 600,the packet handler 48 deletes the call group ID from the current callgroup field 70 of the record held in the PUD 52 for the sender of theend participation request, step 602.

If only one participant then remains in the call, step 604, the lastremaining participant is sent an end-of-call message, step 606, and thecall group ID is deleted from the current call group field in the lastparticipant's record held in the PUD 52, step 608. The unavailablerecipient records are also deleted from the call waiting list in thePUD, and the voice data packets stored in the packet store 50 for thecall group are deleted.

FIG. 12 illustrates a further embodiment of mobile station 700 inaccordance with the present invention. The mobile station 700 includescomponents described in relation to the embodiment of mobile stationillustrated in FIG. 2. These components are referenced with the samereference numerals, and share functionality described in relation to themobile station 8.

The mobile station 700 is therefore capable of conducting GPRS virtualconnection voice calls as described in relation to FIGS. 2 to 11, by theuser operating the keypad 32 and PTT button 34. In addition, the mobilestation 700 is operable in a video conferencing mode.

The mobile station 700 includes an LCD-type display 702, capable ofdisplaying still and video images, in place of the alphanumeric display30 of the mobile station 8. In addition, the mobile station 700 includesa CCD camera 704, capable of picking up still and/or video images, andan image data codec 706, capable of coding and decoding still and/orvideo images in accordance with known still and/or video codingtechniques, such as Jpeg and/or Mpeg-4.

The image data codec 706 interfaces with the GPRS module 19, so as toallow image data to be packetised and depacketised and transferred viathe GPRS radio interface.

The mobile station 700 interacts with the system described in relationto FIG. 2, and in particular the packet handler 48, in the same manneras described in relation to each of FIGS. 6 to 11. Thus, the packethandler is capable not only of forming virtual voice data connectionsfor two-party calls or group dispatch-type calls, but also capable offorming virtual image data connections. The dynamic bandwidth allocationfunctionality provided by GPRS allows the transmission of data at asufficient rate to transmit video data captured by the video camera 704and coded in the image data codec 706, via the GPRS radio interface.

Referring to FIG. 7, when using the mobile station 700 in a videoconferencing mode, the procedures previously described are conducted inorder for the mobile station to set up and seize a video call, and totransmit video and audio data for receipt at one or more call groupparticipants in the PLMN. In this regard, step 208 previously describedin relation to FIG. 7 involves the reception of video data at the videocamera 704 and its conversion in the video codec 706, in addition thepickup of audio data at the microphone 24 and its conversion in theaudio codec 20. Step 210, meanwhile, involves the transmission of bothaudio and video data, either in separate data packets or in the samedata packets, whilst the PTT button 34 remains actuated. In this regard,although referred to as a “PTT” button, this is intended to include a“press to transmit audio and video” button.

In a further mode, the image data accompanying the audio data in step210 is still image data picked up at the camera 704 and coded by theimage data codec 706.

In a yet further mode, the mobile station 700 is arranged to transmitimage data, being video or still image data, alone, in step 210.

The particular mode employed in the mobile station 700 is selectable bythe user of the mobile station via interactions with the man machineinterface, e.g. the keypad 32.

Referring to FIG. 8, the packet handler 48 is capable of performing theprocedures previously described to receive and respond to the call setup request for an image and/or audio call. In this regard, in step 312,the packet handler may receive image data packets and/or voice datapackets during seizure of a call by a recipient. The packet handler 48handles the packets transparently, without regard to the content of thedata packets received.

Referring to FIG. 9, the mobile station 700 is capable of receiving callset up messages, and accepting same, for both image and audio calls. Inthis regard, in step 410, the data packets received via the GPRS radiointerface include image and/or voice data packets, and step 412 involvesthe conversion of those data packets in the image data codec and/or thevoice codec, and the output of images and/or audio signals on thedisplay 702 and/or by the loudspeakers 22.

Thus, this embodiment of the invention provides a method and apparatuswhereby half-duplex video conferencing calls may be conducted, eitherbetween two parties, or in a dispatch mode between groups of callparticipants. It is advantageous, in that video data, which requiresrelatively high amounts of bandwidth, is transmitted only in onedirection at a time, and only intermittently when a user of the systemwishes to transmit image data. In addition, the power requirements forthe mobile station may be relatively low. This is to be contrasted withthe conventional concept of a video conferencing call, in which videodata is transmitted continuously in full duplex mode.

It is to be understood that various modifications and equivalents may beemployed in relation to the embodiments described above, withoutdeparting from the scope of the present invention.

The embodiments for mobile terminal 700 described are operable in both aGPRS virtual connection mode and a conventional circuit-switched mode.Other embodiments of the invention include mobile stations which areoperable only in the GPRS virtual connection mode of the presentinvention.

The GPRS virtual connection mode described above in relation to the twoembodiments of the invention is by nature half-duplex, insofar as onlyone party to the call may transmit voice and/or image data at a time.However, GPRS allows the simultaneous transmission and reception of datapackets via the radio interface, and therefore, in the case of two-partycalls, voice and/or image data transfers may occur at the same time, inorder to provide a full-duplex virtual connection. In this case, neitherof the parties “seizes” the call group, and neither party is preventedfrom transmitting voice and/or image data when receiving such data.

In the above described embodiments, the GGSN 44 transmits logon andlogoff messages to the packet handler 48 when a subscriber attaches anddetaches to the GPRS service. Other signalling procedures are possible.For example, the packet handler 48, when receiving a call set uprequest, may query the HLR and/or the GGSN 44 in order to determine thecurrent status of a potential call participant. Logon/logoff messagesmay also be transmitted to the packet handler 48 from the HLR 12,instead of from the GGSN 44.

In the above described embodiments, control messages passed between amobile station and the packet handler 48 include a call group ID, to bereferenced against the call group records. In the case of a two-partycall, such a call group ID may be replaced by a single recipient ID,referenced to a single recipient record in the PUD 52.

In the above, the packet data network 46 is referred to as an externalpacket data network. The packet data network 46 is ‘external’ insofar asit is beyond the GGSN 44, but it may be under the ownership and controlof the PLMN operator. Thus it may form part of an intranet, or suchlike.It may also take the form of a single physical link between the GGSN 44and the packet handler 48. The functions of the packet handler 48 may beintegrated with those of the GGSN 44.

In the above description, virtual connections between mobile stationsoperating in the same PLMN are controlled by the packet handler. Asillustrated in FIG. 3, a GGSN 56 of another PLMN is also accessible, viathe packet data network 46 from the packet handler. Therefore, thepacket handler may also be used to set up virtual connections betweenmobile stations operating within the PLMN illustrated, and mobilestations operating in other PLMNs which include a GPRS infrastructure.In addition, the packet handler 48 is also able to control virtualconnections between a mobile station operating in the PLMN illustratedand fixed terminals, such as the fixed terminal 58 illustrated in FIG.3, connected to the packet data network 46.

In the above described embodiments, the seizure of a call group, and theperiod for which a mobile station transmits voice and/or image data isdefined by the manual depression of the PTT button 36. Other man machineinterface interactions may also be used to define a call seize operationand the period for which the mobile terminal transmits voice or imagedata, for example those operations and periods may be voice-activated.

In the above described embodiments, the packet store 50 holds datapackets received during a virtual call connection, for potential callparticipants. In addition, the packet store may be used to holdvoicemail messages and data messages received via the GPRS service andto be transmitted onwards via the GPRS service. In addition, the packetstore 50 may hold information to be communicated to user stations viathe GPRS service on request, such as stock price information, news andweather, etc, provided as textual information, still image information,audio information and/or video information.

Embodiments of mobile terminal other than the handsets described areenvisaged. For example, the mobile terminal may be a car telephone,consisting of a GPRS-enabled hardware unit installed in the vehicle anda hand-held microphone/push-to-talk unit connected to the hardware unitvia a wire cord.

In the above, the transfer of audio and image data in half-duplexcommunications modes has been described. The data packets transferred bythe packet handler 48 between user stations may also form textualmessages (short messages) which may be transmitted within the context ofa call, or in a call-independent context. Preferably, the transfer oftext messages is not restricted by the packet handler 48, the packethandler serving only to identify available recipients and recipientaddresses from the PUD 52 for a text message to be transferred, and tostore messages in the packet store 50 for unavailable recipients.

Herein, reference is made to GSM-type systems. Such systems include oneswhich are at least partly based on the GSM system defined in the GSMtechnical specifications published by the European TelecommunicationsStandards Institute (ETSI), such as DCS1800 systems, PCS1900 systems andthird generation systems (such as UMTS) based at least partly on GSM.

It is envisaged that modifications and variations to the above-describedembodiments may be employed, without departing from the scope of theinvention, which is defined in the appended claims.

1. A method of controlling communication between user stations using amobile communications system having a radio interface, said methodcomprising: establishing a call session between a first user station andat least a second user station over said radio interface, wherein thecall session is configured for communication of voice signals betweensaid first and second user stations; providing a data packet handlerconnected to a packet data network, wherein said data packet handler isconfigured to transfer data packets carrying call data between saidfirst user station and said second user station during said callsession; during said call session, receiving requests to transfer datapackets carrying call data between said first user station and saidsecond user station, and dynamically assigning radio resources fortransfer of said data packets over said radio interface, wherein anamount of radio resource assigned varies in accordance with the amountof call data requiring transfer at different times during said callsession as a result of said requests; holding control data relating tosaid call session between said first user station and said second userstation, wherein said control data includes data indicating a state ofsaid call session and data identifying the user stations participatingin said call session; and during said call session, controlling thetransfer of data packets carrying call data between said first andsecond user stations using said data packet handler in accordance withsaid control data.
 2. The method of claim 1, wherein said control dataindicates an existence of said call session.
 3. The method of claim 1,wherein said control data indicates identities of participants in saidcall session.
 4. The method of claim 1, wherein said control dataindicates a seizure of said call session by one of said user stations.5. The method of claim 1, additionally comprising receiving a callsession setup request from said first user station at said packethandler, and transmitting a call session setup confirmation message tosaid first user station.
 6. The method of claim 5, additionallycomprising transmitting a call session setup message to said second userstation from said packet handler, and transmitting said call sessionsetup confirmation message after an acknowledgement is received fromsaid second user station.
 7. The method of claim 1, additionallycomprising accessing a data store from said packet handler to determinean address of said second user station in order to address data packetsto be transmitted thereto.
 8. The method of claim 1, additionallycomprising seizing said call session by said first user station.
 9. Themethod of claim 8, additionally comprising controlling said transfer toprevent the transfer of data packets to said first user station whensaid first user station has seized the call session.
 10. The method ofclaim 8, additionally comprising granting call session seizure to saidsecond user station when said first user station no longer has seizureof the call session.
 11. The method of claim 1, additionally comprisingcopying data packets received from said first user station fortransmission to a plurality of call session participant user stationsincluding said second user station.
 12. The method of claim 1, whereinsaid control data is held in a data store accessible by said data packethandler.
 13. The method of claim 1, wherein said mobile communicationssystem is a GSM-type mobile communications system, said methodcomprising: receiving data packets at said data packet handler from afirst user station via a GPRS data link.
 14. The method of claim 1,wherein said mobile communications system is a GSM-type mobilecommunications system, said method comprising: transmitting data packetsfrom said data packet handler to a second user station via a GPRS datalink.
 15. The method of claim 13, wherein said data packet handler isconnected to a GPRS support node.
 16. A method of handling transfer ofdata in a call session established in a GSM-type mobile communicationssystem between two or more user stations, wherein said transfer of datatakes place between said two or more user stations participating in saidcall session, said method comprising: receiving a first data packet froma first user station, said first data packet containing a recipient ID;mapping said recipient ID to a packet network protocol address, whereinthe packet network protocol address identifies a route to a second userstation via a gateway GPRS support node; and transmitting a second datapacket to said gateway GPRS support node, said second data packetcontaining said packet network protocol address.
 17. The method of claim16, wherein said data packets comprise voice data.
 18. The method ofclaim 16, wherein said data packets comprise still or video image data.19. A data packet handler for a mobile communications system adapted toperform data packet handling functions comprising transfer of datapackets carrying call data between two or more user stationsparticipating in a call session established in the mobile communicationssystem, said data packet handler comprising: a first port to receive andtransmit data packets to and from user stations; a second port tocommunicate with a packet user database to receive call control data,wherein said control data indicates a state of a call session and dataidentifying user stations participating in a call session; and a meansfor processing the data packets, wherein the processing means isconfigured to dynamically assign radio resources for transfer of saiddata packets carrying call data between said two or more user stationsparticipating in a call session, wherein the data packets aretransferred in accordance with said control data, such that an amount ofradio resources varies in accordance with the amount of call data to betransferred.
 20. A mobile station adapted to communicate with a datapacket handler during participation in a call session in which otheruser stations are participating, said mobile station comprising: meansfor dynamically requesting resources for transmission of data packetscarrying call data over a radio interface during a call session to oneor more participating user stations, wherein the amount of radioresources requested varies in accordance with the amount of call data tobe transmitted at different times during said call session; and meansfor transmitting and receiving control data to and from said data packethandler to signal call-related control functions, said control dataincluding data on a status of said call session and/or the identities ofuser stations participating in said call session.
 21. A method ofconducting communications between user stations using a mobilecommunications system, each said user station comprising a camera forpicking up video image of a user and a display for displaying an imageof a remote party, said method comprising: establishing a call sessionbetween participating user stations in which video data transfer cantake place between said user stations at different times during saidcall session, wherein said video data represents a video image picked upby a camera of a participating user station; and during said callsession, controlling said video transfer in a half-duplex mode such thata user station may perform one of either only receiving or onlytransmitting video data for a first period sufficient to receive ortransmit video data that is subsequently used to display a video imageon a display of a receiving user station, and perform the other of onlyreceiving or only transmitting video data for a second period followingsaid first period, sufficient to transmit or receive video data that issubsequently used to display a video image on a display of a receivinguser station.
 22. The method of claim 21, wherein the image datatransmitted and received during the first and second periods forms acomplete image of the user or a remote party.
 23. The method of claim21, wherein said image data comprises video image data, and wherein alength of a period of transmission is variable by the user of the userstation.
 24. A mobile station adapted to participate in a call sessionwith one or more other mobile stations to conduct video communicationswith said one or more other mobile stations, said mobile station havinga half-duplex communications mode for use during a call session that isestablished between said mobile station and one or more other mobilestations, wherein said communications mode is controlled by a dataprocessor which prevents transmission of video data during reception ofvideo data when in said half-duplex communications mode during said callsession and which allows the transmission of video data during a periodof said call session selected by a user.
 25. The mobile station inaccordance with claim 24, wherein said period is selected by anactuation by the user of a switch on said mobile station.
 26. The mobilestation of claim 25, wherein said selected period is defined by a periodof which said switch is manually held by the user.
 27. The mobilestation of claim 25, comprising a data store for storing a groupidentified for transmission in association with the video data, toenable the video data to be transmitted to a plurality of recipient userstations.
 28. A mobile communications station having a group dispatchmode of operation, said station comprising a camera for video datacapture and means for transmitting said video data in said groupdispatch mode.
 29. A method of controlling communication between userstations using a GSM-type mobile communications system, said methodcomprising: establishing a call session between a first and second userstation, wherein the call session is configured for communicationbetween said user stations; providing a data packet handler connected toa GPRS support node for transferring data packets carrying call databetween said user stations during said call session; holding controldata relating to said call session between said first user station andsaid second user station, in a data store accessible by said data packethandler, wherein said control data includes data indicating a state ofsaid call session and data identifying user stations participating insaid call session; and during said call session, controlling thetransfer of data packets between said first and second user stations viaa GPRS data link, using said data packet handler, in accordance withsaid control data.